1. Field of the Invention
The present invention relates to power modules and especially to techniques for improving cooling performance of power modules.
2. Description of the Background Art
FIG. 34 is a schematic external view of a first conventional power module 101P. In the power module 101P, a copper base plate 9P is disposed through a heat-conducting grease (not shown) over a radiating fin or heat sink 2AP, and an insulating substrate 5P is disposed on the base plate 9P. On the insulating substrate 5P, there are disposed a free-wheeling diode 1AP (hereinafter also referred to as xe2x80x9cdiodexe2x80x9d) and an insulated gate bipolar transistor 1BP (hereinafter referred to as xe2x80x9cIGBTxe2x80x9d).
In the conventional power module 101P, copper foils 6P are placed on both main surfaces of the insulating substrate 5P. The base plate 9P and the copper foil 6P are bonded together with solder, and the diode 1AP and the IGBT 1BT are soldered onto the copper foil 6P. An electrode 3P is provided through an insulating layer 4P over the radiating fin 2AP. Then, predetermined electrical connections are made by wires 7P. The construction including the radiating fin 2AP, the diode 1AP, the IGBT 1BP, and the like is housed in a case (not shown).
The electrode 3P is connected to a bus bar or wiring 91P which extends toward the outside of the case. Outside the case, a current transformer 92P for current detection is attached to the bus bar 91P. Further, a cylindrical capacitor 8P for smoothing direct current is provided outside the case independently of the radiating fin 2P and the like (the connection with the case is omitted in the figure).
FIG. 35 is a schematic external view of a second conventional power module 102P. The power module 102P has no base plate 9P as above described, wherein the insulating substrate 5P is disposed through a heat-conducting grease over the radiating fin 2AP. The power module 102P is in all other aspects identical to the above-mentioned power module 101P.
FIG. 36 is a schematic external view of a third conventional power module 103P. The power module 103P is a so-called power transducer. In the power module 103P, all the diodes 1AP and IGBTs 1BP are disposed on the insulating substrates 5P. A heat sink 2BP of the power module 103P has through holes 2BHP therethrough passing a cooling medium. The power module 103P is in all other aspects identical to the above-mentioned power module 101P.
The conventional power modules 101P, 102P, and 103P have the following problems.
First is low temperature reliability during operation. More specifically, when the thermal expansion coefficient of the heat sink 2AP or 2BP differs from those of the diode(s) 1AP and the IGBT(s) 1BP, thermal stresses responsive to a temperature difference from the freezing point of solder will occur at the solder joints as above described. There is thus a problem of occurrence and progress of cracking at the solder joints through a heat cycle (or temperature cycle) in the use (or operation) of the power module 101P, 102P, 103P and/or a heat cycle by repetitions of start and halt of the power module. Such cracking at the solder joints reduces the longevity of the power module.
To reduce the above thermal stresses, it is contemplated for example to increase solder thickness (e.g., 300 xcexcm or more). However, such increased thickness of solder increases thermal resistance between the heat sink 2AP or 2BP and the diode(s) 1AP and the like. This brings up another problem that the size of the heat sink 2AP or 2BP must be increased.
Further, in the conventional power modules 101P, 102P, and 103P, the distribution of temperature in the insulating substrate(s) 5P, the base plate 9P, and the like due to heat generation in the diode(s) 1AP and the like causes warps or winding in the insulating substrate(s) 5P and the like. When the temperature difference is great, clearance is created between the radiating fin 2AP, 2BP and the base plate 9P and the like. Thus, there is a problem of reduced heat transfer because the heat-conducting grease cannot completely fill in the space between the radiating fin 2AP, 2BP and the insulating substrate(s) 5P or the base plate 9P (due to the incoming air). Another problem is that the occurrence or progress of cracking at the solder joints, described above, may be encouraged. The formation of clearance thus results in deterioration in the reliability of the power module.
To prevent the formation of clearance, it is contemplated for example to make the temperature distribution uniform throughout the insulating substrate(s) 5P and the like, or to increase the rigidity of the insulating substrate(s) 5P and the like by increasing the thickness of the substrate(s) 5P and the like. However, such increased thickness increases thermal resistance between the heat sink 2AP, 2BP and the insulating substrate(s) 5P or the like. This brings up, as has been described, another problem that the size of the heat sink 2AP, 2BP must be increased.
Further, when the diode(s) 1AP and the IGBT(s) 1BP produce a large quantity of heat, the amount of current must be limited in order to ensure reliability since the characteristics of the elements vary with increasing temperature.
Secondly, each of the conventional power modules 101P, 102P, and 103P as a whole is large in size since the current transformer 92P and the cylindrical capacitor 8P are provided independently outside the case for such a module. Besides, the current transformer 92P has the property of becoming large when current to be measured has a large DC component, and also the current transformer 92P makes measurements with errors (about 5%) due to its characteristics changes caused by heat generation.
Thirdly, in the power module 103P, the distances from each of the power semiconductor devices, such as the diode 1AP or the IGBT 1BP, to the electrode 61P connected to the low potential side of the power transducer and to the electrode 62P connected to the high potential side vary according to where that power semiconductor device is located. This causes variations in the inductance of the wiring or wires 7P from one power semiconductor device to another, thereby causing variations in output voltage.
A first aspect of the present invention is directed to a power module comprising: a heat sink; a first power semiconductor device disposed directly on the heat sink; and a capacitor disposed directly on the heat sink.
According to a second aspect of the present invention, in the power module of the first aspect, the heat sink has a plurality of surfaces; and the first power semiconductor device and the capacitor are disposed on different ones of the surfaces of the heat sink.
According to a third aspect of the present invention, in the power module of the first or second aspect, the heat sink has a passage of a cooling medium.
According to a fourth aspect of the present invention, in the power module of either of the first through third aspects, the heat sink has conductivity; and an electrode of the first power semiconductor device and an electrode of the capacitor are directly bonded to the heat sink.
According to a fifth aspect of the present invention, the power module of the fourth aspect further comprises: an insulating substrate disposed on the heat sink; and a second power semiconductor device disposed through the insulating substrate over the heat sink.
According to a sixth aspect of the present invention, the power module of the fourth aspect further comprises: another heat sink; and a second power semiconductor device disposed directly on the another heat sink.
According to a seventh aspect of the present invention, in the power module of the sixth aspect, the another heat sink has conductivity; and an electrode of the second power semiconductor device is directly bonded to the another heat sink. The power module further comprises: an insulating member for insulating the another heat sink from the heat sink and the electrode of the capacitor.
According to an eighth aspect of the present invention, the power module of the seventh aspect further comprises: a conductive member disposed on the insulating member; and a flexible wire connected to the conductive member for providing an electrical connection between the first power semiconductor device and the second power semiconductor device.
A ninth aspect of the present invention is directed to a power module comprising: a capacitor; and a first semiconductor device disposed directly on an electrode of the capacitor.
According to a tenth aspect of the present invention, in the power module of the ninth aspect, the electrode of the capacitor has a passage of a cooling medium.
According to an eleventh aspect of the present invention, the power module of the ninth aspect further comprises: an insulating substrate disposed on the electrode of the capacitor; and a second power semiconductor device disposed through the insulating substrate over the electrode of the capacitor.
According to a twelfth aspect of the present invention, in the power module of either of the fifth through eighth and eleventh aspects, the first power semiconductor device and the second power semiconductor device are electrically connected with each other; the first power semiconductor device forms a lower arm of a power transducer; and the second power semiconductor device forms an upper arm of the power transducer.
According to a thirteenth aspect of the present invention, the power module of the twelfth aspect further comprises: a plurality of arms of the power transducer, including the upper arm and the lower arm; and a coaxial line protruding through a surface on which the first or second power semiconductor device is disposed, the coaxial line including a first electrode for supplying a first voltage to the first power semiconductor device of each of the lower arms and a second electrode for supplying a second voltage to the second power semiconductor device of each of the upper arms, wherein the plurality of arms are angularly spaced at regular intervals about the coaxial line.
A fourteenth aspect of the present invention is directed to a power module comprising: a plurality of heat sinks each having a passage of a cooling medium; a plurality of power semiconductor devices disposed on the heat sinks; and a casing having space and being capable of housing the plurality of heat sinks, wherein the plurality of heat sinks are arranged within the space of the casing, leaving a clearance therebetween, whereby continuous space including the clearance and the passages is formed within the space of the casing.
According to a fifteenth aspect of the present invention, in the power module of the fourteenth aspect, the passages of the heat sinks pass an insulative cooling medium.
In accordance with the first aspect, both the first power semiconductor device and the capacitor are directly disposed on the heat sink. The power module can thus be made lighter and smaller than conventional power modules wherein those components are provided independently. Further, the heat radiating action of the heat sink inhibits not only heat generation in the first power semiconductor device but also the temperature rise in the capacitor. This allows miniaturization of the capacitor, a reduction in inductance, and an increase in longevity.
Disposing both the first power semiconductor device and the capacitor directly on the heat sink also reduces the length of wiring between both of them shorter than that in the aforementioned conventional power modules. Thus, circuit inductance can be reduced. This reduces overshoot voltage at a switching operation of the first power semiconductor device, resulting in a reduction in withstand voltage and loss of the first power semiconductor device. The above short wiring length also reduces the occurrence of electromagnetic noise can be reduced.
Accordingly, a compact, lightweight, and highly reliable power module can be provided.
In accordance with the second aspect, the first power semiconductor device and the capacitor are disposed on different surfaces of the heat sink. This allows a further reduction in the size and weight of the power module as compared with the case of disposing both of them on the same surface. Further, less interference occurs between heat radiation in the first power semiconductor device and that in the capacitor, which improves heat radiating performance of the power module.
In accordance with the third aspect, passing a cooling medium through the passage in the heat sink further improves the cooling capability of the heat sink.
In accordance with the fourth aspect, the heat sink having conductivity can be used as an electrode. This reduces the number of components such as wires on the heat sink and processes related to the formation of such components.
Further, the electrodes of both the first power semiconductor device and the capacitor are directly bonded to the heat sink. That is, the first power semiconductor device and the capacitor are electrically connected with each other through the heat sink. In this case, the electrical connection between both the electrodes becomes shorter than in the case where both the electrodes are connected by wiring or the like. A resultant reduction in circuit inductance leads to a considerable reduction in the aforementioned overshoot voltage and the like.
In accordance with the fifth aspect, the second power semiconductor device is disposed through the insulating substrate over the heat sink. This makes it possible to dispose power semiconductor devices of different potentials together on a conductive heat sink in the formation of the circuit.
In accordance with the sixth aspect, the power module further comprises the second power semiconductor device disposed on another heat sink. The combination of the first and second power semiconductor devices simplifies circuit configuration.
In accordance with the seventh aspect, another conductive heat sink is insulated from the above-mentioned conductive heat sink and the electrode of the capacitor by the insulating member. The first and second power semiconductor devices can thus be set at different potentials without the use of any insulating substrate. This allows a reduction in the number of components by the number of insulating substrates. Further, since the construction including the first power semiconductor device and one heat sink and the construction including the second power semiconductor device and another heat sink are broadly equivalent, the manufacturing cost of the power module as a whole can be reduced. This results in the provision of a low-cost power module.
In accordance with the eighth aspect, when providing an electrical connection between the first and second power semiconductor devices, the flexible wire uses, as a relay or junction point, the conductive member disposed on the insulating member. This inhibits a deflection or the slack of the wire as compared with the case where those power semiconductor devices are directly connected by the flexible wire without the use of the above conductive member. As a result, short circuits due to the slack of the wire can be prevented.
In accordance with the ninth aspect, the first power semiconductor device is disposed directly on the electrode of the capacitor. The power module can thus be lighter and smaller than the conventional power modules wherein both components are provided independently. Further, since the electrode of the capacitor is used as a heat sink, the heat radiating action of the heat sink inhibits not only heat generation in the first power semiconductor device but also the temperature rise in the capacitor.
Disposing the first power semiconductor device on the electrode of the capacitor also makes the electrical connection between both of them considerably shorter than that in the aforementioned conventional power modules. Thus, circuit inductance can be reduced. This reduces overshoot voltage at a switching operation of the first power semiconductor device, resulting in a reduction in withstand voltage and loss of the first power semiconductor device. The above short wiring length also reduces the occurrence of electromagnetic noise.
Accordingly, a compact, lightweight, and highly reliable power module can be provided.
In accordance with the tenth aspect, passing a cooling medium through the passage in the electrode of the capacitor further improves the cooling capability of the power module.
In accordance with the eleventh aspect, the second power semiconductor device is disposed through the insulating substrate over the electrode of the capacitor. This makes it possible to dispose power semiconductor devices of different potentials together over the electrode of the capacitor in the formation of the circuit.
In accordance with the twelfth aspect, a highly reliable power transducer can be provided.
In accordance with the thirteenth aspect, the plurality of arms of the power transducer are angularly spaced at regular intervals about the coaxial line. Thus, the wiring between each arm and the first and second electrodes can be installed in a similar manner. This reduces variations in the output from each arm and variations in the first voltage, thereby offering considerable resistance to malfunctions.
In accordance with the fourteenth aspect, the plurality of heat sinks form continuous space including clearances and the passages in the heat sinks, within the space of the casing. At this time, the cooling medium passes through the passages in the heat sinks faster than when passing through the clearances. This improves the cooling capability of the heat sinks. On the other hand, when the cooling medium passes through the clearances, pressure loss is smaller than when the cooling medium passes through the passages. Thus, higher cooling performance can be achieved with smaller pressure loss.
In accordance with the fifteenth aspect, since an insulative cooling medium passes through the passages of the heat sinks, the power semiconductor devices can be isolated from each other without the use of any insulating substrate even if they are directly disposed on the conductive heat sinks. This allows a reduction in the number of components by the number of insulating substrates. Further, since the constructions each including the power semiconductor device and the heat sink are broadly equivalent, the manufacturing cost of the power module as a whole can be reduced. This results in the provision of a low-cost power module.
The aforementioned power semiconductor devices, which are insulated from each other, can be disposed directly on the conductive heat sinks. This improves heat radiating performance of the power module, thereby improving the reliability of the power module.
It is therefore an object of the present invention to provide a compact, lightweight, and highly reliable power module.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.